CXA2149 查看數據表（PDF） - Sony Semiconductor
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CXA2149 Datasheet PDF : 25 Pages
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CXA2149Q
Video System Notes
1. 200 kHz is taken to be 0 dB for the purpose of this measurement. Where applicable, the group delay
function will be turned off to make this measurement.
2. Weighted using CCIR567.
3. This group delay characteristic, figure 1, is for the B, G specifications. It does not take into account the
input and output delays inherent within the AV switch.
4. The sync detection circuits operate on the video sources that have been switched into the TV and CVIN1
channels, respectively.
The internal SYNC discriminator circuit functions in the following way. The SYNC tip of the incoming video
input is clamped to a fixed level and the signal is then compared in magnitude with an internal threshold
voltage. If the signal is smaller than the threshold level the IC determines that the SYNC does not exist.
Conversely, if the signal is found to be greater than the threshold then the duty cycle of signal is passed to
the duty discrimination circuit. The discriminator circuit will identify whether the duty cycle of the signal is
above 91 % at which point SYNC is detected, or below 84 % when SYNC is not detected.
To prevent occasional video disturbances such as IF noise from the tuner causing malfunctioning of the
SYNC detector, a time constant of approximately 14 line periods is applied during which the status of the
SYNC detection is maintained.
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